Topical medicament allergy: the importance of patch testing

A 41-year-old woman with a 6-year history of mild psoriasis presented with a rash under her breasts. She was prescribed Trimovate cream (GlaxoSmith Kline) and had a florid weeping eczema within 48 hours of application. This settled with the withdrawal of Trimovate. Contact dermatitis is type IV allergy and usually appears within 2-3 days after contact with an external allergen. Detection of the allergen, or allergens, is important, as avoidance results in resolution of the eczema. Our patient was patch tested and showed positives to three components of Trimovate; cetearyl alcohol, sodium metabisulphite, and clobetasone butyrate. These are important allergens to identify, because they are also present in other products. Clobetasone butyrate is often used in facial and flexural psoriasis. Cetearyl alcohol is particularly significant, as it is found in many products including commonly used moisturizers such as Diprobase (MSD), Cetraben (Genus) and Epaderm (Molnlycke) cream, and most steroid creams. Our patient highlights the fact that is insufficient to simply advise a patient to avoid the topical medicament that has caused a reaction. Patch testing is necessary to identify which components the patient is allergic to, so that they can be avoided in all products. This is of particular significance for our patient given her history of psoriasis, as she will likely require moisturizers and topical steroid preparations in the future. Since she began avoiding these allergens, she has had no recurrence of eczema. To conclude, GPs should consider sending their patients with contact dermatitis for patch testing, as the identification of all allergens is valuable to management. Keywords: patch testing, contact dermatitis, concomitant sensitivity, Trimovate cream, sodium metabisulphite, clobetasone butyrate, cetearyl alcohol.